Components which are exposed to high temperatures and corrosive conditions must be provided with special coatings, in order to protect them against damage and therefore ensure a longer service life. Currently, in particular for components of steam or gas turbines, coating systems are used which consist of a plurality of layers applied on one another. These often comprise at least one bonding coat, which is applied directly on the component, and a thermal barrier coat applied thereon.
In many cases the bonding coat has the general composition MCrAlY, where M stands for at least one of the elements in the group comprising iron, cobalt and nickel, and Y is yttrium or another equivalent element in the group comprising scandium and the rare earth elements. The purposes of the bonding coat are on the one hand to protect against corrosion and/or oxidation and on the other hand to ensure strong bonding of the thermal barrier coat on the component.
The thermal barrier coat in turn often consists of ceramic materials, which may contain zirconium oxide. Only its capacity for strong thermal insulation makes it possible to use the components in temperature ranges >1000° C.
Corresponding protective coats and coat systems are described, for example, in EP 1 541 713 A1.
In the known bonding coats, inter-diffusion phenomena between the metal alloy of the base material of the component and the constituents of the bonding coat may take place in a temperature range >550° C., so that undesired phase formation may occur. This entails degradation of the base material properties, which reduces the service life of the component. Minimal inter-diffusion of the alloy elements between the bonding coat and the base material, which does not degrade the properties of the base material, is nevertheless desirable since the bonding between the base material and the bonding coat is thereby improved significantly. Furthermore, the oxidation and corrosion behavior of the base material in the superficial region can be improved in this way.